Conclusion
The Inca’s are one of the most civilized group of Indians trough history, they had huge secrets which may not have been found yet.
They were a large gathered group of people and may just have been the rulers of the whole of South-America.

Sources:

Facts

http://en.wikipedia.org/wiki/Inca_Empire
http://www.crystalinks.com/incan.html
http://en.wikipedia.org/wiki/Inca_civilization'

Pictures:
sources are linked to on every picture.